The subject invention relates to a roofing system for roof decks that are able to retain mechanical fasteners, and in particular to an insulated roofing system and method of constructing the insulated roofing system that utilizes unique hold-down straps to secure the roof insulation to the roof deck. The invention is especially suited for use in EPDM, PVC, and TPO membrane roofing systems, modified bitumen roofing systems, and built-up roofing systems utilizing multiple layers of bitumen and roofing felts.
Industrial, commercial, and similar buildings typically have low slope roof decks. The two major types of industrial/commercial roofing systems utilized on these roof decks are single ply roofing membrane systems and built-up roofing systems that include multiple layers of bitumen and roofing felts. Normally, these roofing systems include roof insulation boards that are located beneath the membrane or bitumen and felt layers of the roofing system and over the roof deck. The typical roof insulation boards used to insulate these roofing systems are 4×8 foot, 4×4 foot, 3×4 foot and 2×4 foot expanded perlite, fiberglass, wood fiber, and closed or open cell foam insulation boards. An example of 2×4 foot and 4×4 foot, 0.75 to 2.0 inch thick, expanded perlite insulation board that may be used as the insulation board in such systems is an expanded perlite insulation board sold by Johns Manville International, Inc. under the trade designation Fesco® Board Roof Insulation. An example of 4×4 foot and 4×8 foot, 1.0 to 4.0 inch thick closed cell foam insulation board that may be used as the insulation board in such systems is a closed cell polyisocyanurate foam core board sold by Johns Manville International, Inc. under the trade designation UltraGard® ISO 1,2,3™ Roof Insulation. An example of a gypsum insulation board is a gypsum insulation board sold by Georgia-Pacific Corporation under the trade designation Dens-Deck® glass mat gypsum roof board.
Many roof decks, including but not limited to steel, wood, and lightweight concrete roof decks, can accept and retain conventional mechanical fasteners. When insulated single ply roofing membrane systems and insulated built-up roofing systems are being installed over roof decks that can accept and retain conventional mechanical fasteners, the roof insulation boards are normally secured to the roof deck with mechanical fasteners. To conform to industry standards, such as Factory Mutual standards, Underwriters laboratories, Inc. standards and code agency standards for wind-resistant systems (systems that can withstand certain specified wind velocities without uplift of the roof insulation boards or the fasteners pulling-through the roof insulation boards), these 4×8 foot, 3×4 foot, 4×4 foot, and 2×4 foot expanded perlite, fiberglass, wood fiber, and foam roof insulation boards are typically secured to the roof deck with up to 24 conventional mechanical fasteners per roof insulation board. While this system for securing the roof insulation boards to roof decks works well, the system has two drawbacks. The relatively large number of mechanical fasteners required to anchor the roof insulation boards to achieve wind-resistant systems that meet industry standards and the time required to install the roof insulation boards utilizing such a relatively large number of mechanical fasteners are costly to the contractor and building owner. Accordingly, there has been a need for a system to anchor roof insulation boards to a roof deck that can be assembled more quickly with fewer mechanical fasteners while providing equal or greater wind uplift resistance.